1. Field of the Disclosure
The present disclosure is directed generally to abrasive particulate materials and particularly, abrasive particulate materials for use in polishing applications and other applications.
2. Description of the Related Art
Abrasive particulate materials are used in a wide range of applications, for example grinding, polishing and finishing surfaces in a variety of applications. Abrasive powders can be utilized in dry or wet form, wherein utilizing the abrasive powders in a wet form typically requires the dispersion of the powder in a solvent to create an abrasive slurry. Particular abrasive slurries are commonly used in polishing applications, such as chemical mechanical planarization (CMP) in the semiconductor device manufacturing industry.
Characteristics of abrasives relevant to polishing applications, such as CMP include material removal rate, selectivity and defectivity. Material removal rate is a measure of the capability of the abrasive slurry to remove material, over a length of time under fixed polishing conditions. Selectivity is a measure of the ability of the slurry to remove one type of material (e.g., a metal), while leaving a portion or substantial portion of another material intact (e.g., a dielectric). The selectivity of an abrasive slurry is particularly relevant in the semiconductor device manufacturing industry where it is desirable to uncover layers, or portions of layers, underlying a layer of different material, leaving behind a planar composite surface.
A common problem associated with slurries is that the particles are predisposed to settling or forming an unstable suspension. Often, additives or other stabilizers are added to the slurry to improve the stability and hold the particles in suspension. However, shipping and storing a stabilized slurry are expensive and cumbersome propositions because of the additional weight of the water and additives. As such, it is not preferable to ship and/or store slurries. Naturally, the extra processing and additional materials added to a slurry to stabilize or re-stabilize the suspension are costs that ideally could be reduced or avoided.
One industry approach focuses on improving material removal rates and reducing polishing times, and as such, has made use of the high temperature phase of alumina, alpha alumina. Alpha alumina may be formed through conversion of an aluminous precursor, typically at a temperature on the order of 1000° C. to 1200° C. See, for example, Harato et al. (U.S. Pat. No. 5,302,368) and Kaisaki et al. (U.S. Pat. No. 6,194,317). Alpha alumina may be formed at lower temperatures by thermally converting a hydrated form of alumina to a transition phase (gamma phase) alumina and grinding to seed the transition phase with a corundum phase (alpha alumina). See “Effect of mechanochemical activation on the thermal reactions of boehmite (γ-AlOOH) and γ-Al2O3”, MacKenzie, K. J. D., Temuujin, J, Smith, M. E., Angerer, P., Kameshima, Y., Thermochimica Acta 359 (2000) 87-94.
Abrasive compounds containing primarily alpha alumina are useful in polishing metal surfaces at high material removal rates. While alpha alumina is the hardest phase of polycrystalline alumina and provides a desirably high material removal rate, its use is limited to certain applications due to poor selectivity and tendencies to produce undesirable surface defects such as scratches and orange peel.
In an effort to reduce the surface defects and poor selectivity of slurries containing primarily alpha alumina particles, softer forms of abrasive particles (e.g., aluminum hydroxides and transition aluminas) have been combined with alpha alumina particles. See for example, Wang et al. (U.S. Pat. No. 5,693,239). However, such slurries have been characterized as having limited specific surface area, and testing has revealed generation of considerable surface defects in CMP applications.
Other abrasives compounds and abrasive slurries have been formed to contain principally softer crystalline particles (relative to alpha alumina, such as transition aluminas). See for example, Chelle (U.S. Pub. No. 2005/0194358), which discloses a high purity fumed gamma alumina particles. Still, other abrasives have included softer alumina crystalline particles in addition to other compounds, such as cerium oxide. See for example, Sakatani et al. (U.S. Pat. No. 5,804,513) and Ueda et al. (U.S. Pat. No. 5,697,992). Such materials are generally heterogeneous (having both alumina and another metal oxide), are limited to gamma transition alumina particles, and have low specific surface areas and large particle sizes, characteristics that affect the polishing performance and stability of the material in a slurry.
The art has also combined amorphous phase aluminum oxide and a crystalline transition alumina phase. See for example, Neville et al. (U.S. Pat. No. 5,527,423) which discloses a material containing an amorphous phase and a gamma alumina phase. Such material is characterized by a high dry powder density. Inspection of actual samples obtained in accordance with the disclosure of the '423 patent has revealed a powder density of 3.78 g/cm3, which impacts slurry stability and polishing performance.
The art has also reported gamma phase transition alumina with limited chi phase transition alumina. See for example, Thome et al., U.S. Pat. No. 5,413,985 disclosing a process of shock calcining hydragillite to form a partially crystalline transition alumina of both 4-fold and 5-fold coordination.
The industry continues to demand abrasive particulate materials that provide high selectivity with attendant desirable material removal rates. In addition, the industry also needs materials that are capable of being stored or shipped in dry form and capable of being dispersed in a solvent to form a stable, ready-to-use slurry with minimal stabilizing processing. Alternatively, instead of dry powder, the industry would benefit from alumina suspensions that are colloidally stable (exhibiting little or no sedimentation after extended periods).